Getting last read value on 2100

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vsurija
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Getting last read value on 2100

Post by vsurija » October 14th, 2015, 11:28 pm

Hi,
Is there a way to make K2100 DMM to trigger itself to read voltage on max resolution (slow 6 1/2 digits), and just to collect last data point via SCPI? I need just one value, it does not have to be synchronized (triggered) with other readings, but I need it fast.
Normal reading takes about 220 milisecs (READ? or INIT/FETC?), but sometimes I have to read even faster then that, but I don't care if I get an old (stale) data or not, since at this principle all other instruments in my setup work.

Best regards,
Vinko

Norbert W
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Re: Getting last read value on 2100

Post by Norbert W » October 15th, 2015, 2:29 am

Hello,

with a model 2000 you could use a fetch? to do this job.

The model 2100 uses a combination of init / fetch?
So you might send an init whenever you want to start a conversion -
but in case you need a reading before the init send a fetch? first.
Not sure if this fits your complete setup because you would be stuck if you started a conversion and shortly afterwards
look for an old reading. This said you would need to have a good timing control in your program to overlook when starting
a new measurement is allowed to happen ...

vsurija
Posts: 5
Joined: October 14th, 2015, 10:59 pm
Country: Croatia

Re: Getting last read value on 2100

Post by vsurija » October 15th, 2015, 3:47 am

Hi,
Thank you for an answer, but maybe I wasn't clear enough.
I wish to achieve that the 2100 is in AUTO-TRIGGER mode (like when used on front panel), but to read data remotely. As far as I see, this is not possible, since when instrument goes in REMOTE mode, its trigger goes to WAIT-FOR-TRIGGER state, and I have to send INIT command, or READ? command to initiate the measurement.
On SLOW 6 1/2 digits, integration time is 10 PLC (200 ms), and with some communication overhead, total time cost is about 220-250 ms.
If I query (send, and wait for an answer) instrument with READ? command, my program halts while waiting for an answer for cca 250ms. If I send INIT command, and some time later query with FETCh? command, time to respond varies depending if the measurement is done or not. If it's done, then the response time is quick, but if it's not, than it waits for measurement to finish, and then it responds.
Is there any way (undocumented feature :) ) to make the instrument to self-trigger and just to collect last reading (regardless if it's fresh or not), since other Keithley instruments in our setup support this, or this is a limitation of budget version DMM?

Best regards,
Vinko

Dale C
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Re: Getting last read value on 2100

Post by Dale C » October 15th, 2015, 7:26 am

What about using the Immediate trigger and just sending FETCH? when you need a measurement?
Here is the command
TRIGger:SOURce IMMediate
:FETCH?
Maybe that would help.

vsurija
Posts: 5
Joined: October 14th, 2015, 10:59 pm
Country: Croatia

Re: Getting last read value on 2100

Post by vsurija » October 15th, 2015, 10:43 pm

Hi Dale,
I have tried your suggestion, and it does not work. Here is log from Keithley Communicator:

Code: Select all

*IDN?
KEITHLEY INSTRUMENTS INC.,MODEL 2100,1,01.08-01-01
:SYST:ERR?
+0,"NO ERROR"

READ? // Instrument can normally read voltage?
-1.72986368E-01 // Yes
:SYST:ERR?
+0,"NO ERROR"

TRIGGER:SOURCE IMMEDIATE
:SYST:ERR?
+0,"NO ERROR"
TRIGGER:SOURCE?
IMM
:SYST:ERR?
+0,"NO ERROR"

:FETCH?
Timeout expired before operation completed
:SYST:ERR?
-230,"Data stale" // No initial trigger

INIT // Trigger new measurement
:SYST:ERR?
+0,"NO ERROR"

:FETCH?
-1.30476560E-01 // New value
:SYST:ERR?
+0,"NO ERROR"
// I waited here few seconds

:FETCH?
-1.30476560E-01 // No new measurements triggered
:SYST:ERR?
+0,"NO ERROR"
// I waited here few seconds
INIT
:SYST:ERR?
+0,"NO ERROR"

:FETCH?
-7.72419264E-01 // New value
:SYST:ERR?
+0,"NO ERROR"
READ?
-9.45665216E-01 // New value
:SYST:ERR?
+0,"NO ERROR" 
As you can see from this example, the :FETCh? command does retrieve the latest measured value (the same one on instrument display), but the only way I could get instrument to perform a new measurement is either by sending INIT or READ? command.

Is there any other way for instrument to trigger itself while in REMOTE mode?

P.S. This procedure normally works on our K2700 DMM and K2182A, since they can trigger itself while in REMOTE mode.

P.S. 2: I have also tried to put instrument to LOCAL mode by :SYSTEM:LOCAL, wait for instrument to display new value on its display, and then to read value with :FETCH?, but I always get the last value triggered with INIT command, not the one displayed on front panel.



Best regards,
Vinko

Dale C
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Re: Getting last read value on 2100

Post by Dale C » October 16th, 2015, 5:45 am

VInko,
I thought that would work. I found that command in the manual and it seemed like that was what you needed.
Sounds to me like the 2100 does not follow the strict rules of SCPI.
The Model 2000 would do what you need for sure.
Dale

vsurija
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Joined: October 14th, 2015, 10:59 pm
Country: Croatia

Re: Getting last read value on 2100

Post by vsurija » October 16th, 2015, 6:08 am

Hi Dale,
I figured that it isn't 100% compatibile. The problem is that we have in our setup 2100, not 2000...
Is there any workaround for this problem?
Will there be some sort of firmware update that will address this issue?

ATB,
Vinko

Dale C
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Re: Getting last read value on 2100

Post by Dale C » October 16th, 2015, 1:09 pm

We can enter a “bug or enhancement” request and we will review. However can't promise we will fix quickly since changing f/w on a mature product is time consuming and could potentially break other things.
The quickest solution is to move to the 2000 and we will try to work some kind of deal to minimize the price differential between these models . regards,
Dale

vsurija
Posts: 5
Joined: October 14th, 2015, 10:59 pm
Country: Croatia

Re: Getting last read value on 2100

Post by vsurija » October 21st, 2015, 5:37 am

Thank you for your offer, but for the moment we will have to stick with 2100 for other reasons.
I understand that this could be a breaking change in firmware update, but if there is a way to correct this issue, than firmware update is all we need.
Maybe it is not a bad idea to point this "feature" out in instrument specifications or white paper, so future customers are aware of this?

Best regads,
Vinko

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